Magnetoresistive device and magnetic component

ABSTRACT

A magnetoresistive device including a high-resistivity layer ( 13 ), a first magnetic layer ( 12 ) and a second magnetic layer ( 14 ), the first magnetic layer ( 12 ) and the second magnetic layer ( 14 ) being arranged so as to sandwich the high-resistivity layer ( 13 ), wherein the high-resistivity layer ( 13 ) is a barrier for passing tunneling electrons between the first magnetic layer ( 12 ) and the second magnetic layer ( 14 ), and contains at least one element L ONC  selected from oxygen, nitrogen and carbon; at least one layer A selected from the first magnetic layer ( 12 ) and the second magnetic layer ( 14 ) contains at least one metal element M selected from Fe, Ni and Co, and an element R CP  different from the metal element M; and the element R CP  combines with the element L ONC  more easily in terms of energy than the metal element M. Accordingly, a novel magnetoresistive device having a low junction resistance and a high MR can be obtained.

This application is a divisional of application Ser. No. 09/744,513,filed Jan. 24, 2001, which is a 371 of PCT/JP00/03452, filed on May 29,2000, which application(s) are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a magnetoresistive device and a methodfor producing the same, and a magnetic component.

BACKGROUND ART

A TMR (tunnel magnetic resistance) device is a device in which a verythin insulating layer is inserted between two ferromagnetic layers. ATMR device uses the phenomenon that the tunneling current flowingthrough the insulating layer is changed by the relative angle ofmagnetization of each metal element M.

It has been expected in theory that when using a ferromagnetic metalelement M having a high spin polarizability such as Fe or FeCO for theferromagnetic layers, a high rate of change in magnetic resistance of atleast 35% is obtained (M. Jullier, Phs. Lett. 54A (1975) 225). However,a high MR (magneto resistance) has not been possible to realize.

Recently, Miyazaki et al. reported that they produced an insulatinglayer of alumina by natural oxidation in the air, and obtained a highrate of change in MR (T. Miyazaki and N. Tezuka, J. Magn. Magn. Mater.139 (1995) L231). With this report, active development of TMR materialsand TMR devices has started.

The recently reported methods for producing insulating layers showing ahigh MR are classified largely into two methods. One is a naturaloxidation method in which an aluminum film formed on a ferromagneticfilm is oxidized in the air or in pure oxygen (Tsuge et al., Document ofthe 103rd Workshop by the Society of Applied Magnetics of Japan, p. 119,(1998)). The other is a plasma oxidation method in which an aluminumfilm formed on a ferromagnetic film is oxidized in an oxygen plasma (J.S. Moodera et al. Phy. Rev. Lett., 74, 3273 (1995)).

To obtain a high MR, these TMR devices use a transition metal showing ahigh spin polarizability such as Fe or CoFe for the lower ferromagneticlayer on which the aluminum film is formed.

Because the current flowing in a TMR device is mainly a tunnelingcurrent through an insulating layer, the resistance of the device issubstantially high. Thus, when a TMR device is used as a reproducinghead or MRAM, S/N ratio decreases due to thermal noise, and thresholdfrequency of a readout circuit decreases during a fast response.

To lower the resistance of the device, reducing the film thickness ofthe alumina insulating layer could be considered. However, with aconventional process for oxidizing an aluminum film, the lowerferromagnetic film is likely to be oxidized beyond the aluminum filmwhen the aluminum film is thin. As a result, when antiferromagneticmaterials such as Fe₂O₃ and CoO are formed at the interface with thealuminum oxide film by an excess oxidation reaction, for example, due tothe interaction with these antiferromagnetic oxides, tunneling electronslose information of magnetization direction with an external magneticfield.

On the other hand, when the aluminum film is not oxidized completely anda portion of the aluminum film remains, the spin memory of the tunnelingelectrons passing through the remaining aluminum film is lost, and MR isreduced.

Furthermore, in conventional TMR devices, when a large bias is applied,the rate of change in MR is decreased greatly due to generation ofmagnon, etc.

Furthermore, conventional MR devices do not have a sufficient thermalstability, and for example, when using them as MRAM, heat deteriorationsuch as decreased MR property is caused during post-annealing of CMOS(at about 250 to 400° C.) or heating in the production of MR heads (atabout 250° C.), or during its use.

DISCLOSURE OF THE INVENTION

In view of the above-mentioned problems, it is an object of the presentinvention to provide a new magnetoresistive device having a low junctionresistance and a high MR and a method for producing the same, and amagnetic component.

To achieve the above object, the present invention provides amagnetoresistive device including a high-resistivity layer, a firstmagnetic layer and a second magnetic layer, the first magnetic layer andthe second magnetic layer being arranged so as to sandwich thehigh-resistivity layer, wherein the high-resistivity layer is a barrierfor passing tunneling electrons between the first magnetic layer and thesecond magnetic layer, and contains at least one element L_(ONC)selected from oxygen, nitrogen and carbon; at least one layer A selectedfrom the first magnetic layer and the second magnetic layer contains atleast one metal element M selected from Fe, Ni and Co, and an elementR_(CP) different from the metal element M; and the element R_(CP)combines with the element L_(ONC) more easily in terms of energy thanthe metal element M. In the magnetoresistive device of the presentinvention, the element R_(CP) contained in the layer A combinesselectively with the element L_(ONC) diffusing from the high-resistivitylayer to form a compound. Thus, in the magnetoresistive device of thepresent invention, oxidation, nitriding or carbonization of the metalelement M can be inhibited, thereby preventing generation of a localizedspin resulting in spin inversion. Furthermore, when the element R_(CP)in the layer A combines with the element L_(ONC) to form a compound, thecompound itself functions as a part of the high-resistivity layer. Inaddition, because the diffusion velocity of oxygen ions or nitrogen ionsin the compound of the element R_(CP) and the element L_(ONC) issubstantially lower than in the magnetic films, the compound of theelement R_(CP) and the element L_(ONC) acts as a layer to inhibitdiffusion of excess oxygen or nitrogen. Therefore, in themagnetoresistive device of the present invention, formation of ahigh-resistivity layer having a larger thickness than necessary,resulting in an increase in the resistance of the device, is inhibited.Thus, according to the magnetoresistive device of the present invention,a device having a low junction resistance and a high MR is obtained.

In the magnetoresistive device of the present invention, it ispreferable that the layer A contains the element R_(CP) so that aconcentration of the element R_(CP) is high on the side of thehigh-resistivity layer. When the element R_(CP) is in a solid solutionstate with a metal composed of the metal element M, its spinpolarizability is generally lower than that of the single metal composedof the metal element M. However, by making the concentration of theelement R_(CP) high on the side of the high-resistivity layer in thelayer A, the element R_(CP) forms a compound, and the element R_(CP) andthe metal element M are separated in phase. As a result, high spinpolarizability is obtained in the vicinity of the high-resistivitylayer, which has the greatest influence on the rate of change inmagnetoresistance. The spin polarizability can be increased bydecreasing the concentration of the element R_(CP) as it is farther fromthe high-resistivity layer. The layer A may have a two-layered structuresuch as an element R_(CP)-containing Fe layer/Fe layer from the side ofthe high-resistivity layer. The layer A also may have a structure suchas an element R_(CP)-containing FeCo layer/FeCo layer from the side ofthe high-resistivity layer.

In the magnetoresistive device of the present invention, it ispreferable that the element R_(CP) is at least one element selected fromSi, Ge, Al, Ga, Cr, V, Nb, Ta, Ti, Zr, Hf, Mg and Ca. These elementshave a larger free energy in negative for forming oxides than the metalelement M, and selectively capture oxygen ions or nitrogen ionsdiffusing from the high-resistivity layer. Among these elements, Si, Al,Cr and Ti have particularly large diffusion constants in metal elements.Thus, these four elements diffuse toward the side of thehigh-resistivity layer so that their concentrations are high on the sideof the high-resistivity layer, using as a driving force the chemicalpotential gradient of the oxygen or nitrogen ions generated when formingthe high-resistivity layer. Therefore, a desirable concentrationgradient of the element R_(CP) can be formed easily by using these fourelements. This self-diffusion of elements tends to appear moreremarkably when the high-resistivity layer is formed at a higherreaction temperature.

In the magnetoresistive device of the present invention, it ispreferable that the layer A consists of Fe, Si and Al. Accordingly, alower resistance of the device can be obtained. Furthermore, the rate ofchange in the magnetoresistance is increased, and the soft magneticproperty of the layer A is enhanced. Thus, a high MR is obtained at alow magnetic field.

In the magnetoresistive device of the present invention, it ispreferable that the element R_(CP) forms a compound with the elementL_(ONC) in the vicinity of the high-resistivity layer in the layer A.Accordingly, the spin polarizability in the vicinity of thehigh-resistivity layer is increased due to phase separation with themetal element M, so that a magnetoresistive device having a particularlyhigh rate of change in magnetoresistance is obtained.

In the magnetoresistive device of the present invention, it ispreferable that the second magnetic layer is formed after forming thehigh-resistivity layer, and a portion of the high-resistivity layercontacting the second magnetic layer contains an aluminum oxide as amain component. Oxygen and nitrogen ions have a lower diffusion constantin an aluminum oxide than in other oxides. Thus, according to the abovestructure, diffusion of these ions through the high-resistivity layercan be inhibited effectively when forming the high-resistivity layer. Asa result, the probability that the element R_(CP) captures oxygen andnitrogen ions diffusing through the high-resistivity layer increases, sothat oxidation and nitriding of the metal element M resulting in spininversion can be inhibited. Furthermore, according to the abovestructure, the thickness of the high-resistivity layer is controlledeasily. Furthermore, in the above structure, it is preferable that acurrent is passed so that the first magnetic layer is positive and thesecond magnetic layer is negative. Accordingly, diffusion of oxygen ionsis inhibited when a current is applied, so that the life of the devicecan be extended.

In the magnetoresistive device of the present invention, it ispreferable that at least a portion of the high-resistivity layer isformed by forming a film containing the metal element M and the elementR_(CP), and then reacting the surface of the film with the elementL_(ONC). Accordingly, is the element R_(CP) in the first magnetic layerand the high-resistivity layer form a thermally stable relationship, sothat the reliability of the device at a high temperature is increased.Furthermore, in this case, it is preferable that a current is passed sothat the first magnetic layer is negative and the second magnetic layeris positive. Accordingly, diffusion of oxygen ions is inhibited when acurrent is applied, so that the life of the device can be extended.

Furthermore, the present invention provides a method for producing amagnetoresistive device, including:

(a) forming a first magnetic layer located on a substrate, and ahigh-resistivity layer located on the first magnetic layer andcontaining at least one element L_(ONC) selected from oxygen, nitrogenand carbon; and

(b) forming a second magnetic layer on the high-resistivity layer;wherein the first magnetic layer contains at least one metal element Mselected from Fe, Ni and Co, and an element R_(CP) different from themetal element M; and the element R_(CP) combines with the elementL_(ONC) more easily in terms of energy than the metal element M.According to the method of the present invention, a magnetoresistivedevice of the present invention can be produced.

In the method of the present invention, it is preferable that the step(a) includes:

(a-1) forming a magnetic layer containing the metal element M on thesubstrate, and

(a-2) forming a layer B containing the element R_(CP) on the magneticlayer, and then reacting a portion of the layer B on the side of itssurface with the element L_(ONC) thereby to form the high-resistivitylayer, and further includes:

after the step (a-2) and before or after the step (b), allowingunreacted parts of the element R_(CP) in the layer B and the metalelement M in the magnetic layer to diffuse mutually by heating thesubstrate at a temperature of at least 50° C. but not higher than 350°C., thereby to form the first magnetic layer in which the concentrationof the element R_(CP) gradually increases to the side of thehigh-resistivity layer. Accordingly, unreacted parts of the elementR_(CP) are allowed to diffuse into the first magnetic layer, so thatdeletion of spin memory due to unreacted parts of the element R_(CP) canbe prevented.

In the method of the present invention, it is preferable that the step(a) includes:

(a-1) forming the first magnetic layer on the substrate; and

(a-2) forming a layer C having a thickness of 0.1 nm to 2 nm andcontaining the element R_(CP) on the first magnetic layer, and thenreacting the layer C with the element L_(ONC) thereby to form thehigh-resistivity layer. Accordingly, when forming the high-resistivitylayer, the element R_(CP) in the first magnetic layer captures theelement L_(ONC) diffusing from the high-resistivity layer to form acompound. Thus, a magnetoresistive device having a low junctionresistance and a high MR is obtained.

In the method of the present invention, it is preferable that in thestep (a-2), the element R_(CP) in the layer C is allowed to diffuse intothe first magnetic layer so that the concentration of the element R_(CP)gradually increases to the side of the high-resistivity layer in thefirst magnetic layer.

In the method of the present invention, it is preferable that the step(a) includes:

(a-1) forming the first magnetic layer on the substrate;

(a-2) depositing the element R_(CP) on the first magnetic layer in a gasatmosphere containing the element L_(ONC) thereby to form thehigh-resistivity layer. Accordingly, the magnetoresistive device of thepresent invention can be produced easily.

In the method of the present invention, it is preferable that in thestep (a-2), the element R_(CP) is allowed to diffuse into the firstmagnetic layer so that the concentration of the element R_(CP) graduallyincreases to the side of the high-resistivity layer in the firstmagnetic layer.

In the method of the present invention, it is preferable that the step(a) includes:

(a-1) forming a magnetic layer containing the metal element M and theelement R_(CP) on the substrate; and

(a-2) reacting the surface of the magnetic layer with the elementL_(ONC) thereby to form the first magnetic layer and thehigh-resistivity layer. According to this method, even when the surfaceof the magnetic layer is not flat, a high-resistivity layer having anapproximately uniform thickness can be formed easily. Furthermore, inthis method, it is preferable that in the step (a-2), the element R_(CP)is allowed to diffuse into the first magnetic layer so that theconcentration of the element R_(CP) gradually increases to the side ofthe high-resistivity layer in the first magnetic layer. Furthermore, inthis case, it is preferable that in the step (a-2), when reacting thesurface of the magnetic layer with the element L_(ONC), the surface ofthe magnetic layer is heated at a temperature of at least 50° C. but nothigher than 800° C. By carrying out such a heating, the diffusionvelocity of the element R_(CP) can be increased, and the time forforming the high-resistivity layer can be shortened.

In the method of the present invention, it is preferable that in thestep (a), the first magnetic layer is formed by evaporation orsputtering so that the concentration of the element R_(CP) is high onthe side of the high-resistivity layer in the first magnetic layer.Accordingly, the concentration distribution of the element R_(CP) in thefirst magnetic layer can be controlled easily by controlling thedeposition rate of the element R_(CP).

Furthermore, the present invention provides a magnetic componentincluding a magnetoresistive device, wherein the magnetoresistive deviceis obtained by heating the magnetoresistive device of the presentinvention at a temperature of at least 200° C. According to the magneticcomponent of the present invention, each magnetic component easily canobtain an arbitrary resistance meeting its use as well as a high MR. Forexample, a resistance of several ten-ohms to several mega-ohms timessquare micron for RA (resistance area) is required in MRAM. Also, aresistance of several tens of milli-ohm to several ohms times squaremicron is required in a magnetic head. Moreover, a high MR can beobtained even when its surface is relatively rough.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a plan view showing an example of a magnetoresistive deviceof the present invention. FIG. 1(b) is a sectional view of themagnetoresistive device of FIG. 1(a).

FIG. 2(a) is a plan view showing another example of a magnetoresistivedevice of the present invention. FIG. 2(b) is a sectional view of themagnetoresistive device of FIG. 2(a).

FIG. 3 is a process drawing showing an example of a method for producinga magnetoresistive device of the present invention.

FIG. 4 is a process drawing showing another example of a method forproducing a magnetoresistive device of the present invention.

FIG. 5 is a process drawing showing still another example of a methodfor producing a magnetoresistive device of the present invention.

FIG. 6 is a process drawing showing still another example of a methodfor producing a magnetoresistive device of the present invention.

FIG. 7(a) is a partially sectional view showing still another example ofa magnetoresistive device of the present invention. FIG. 7(b) is aschematic illustration showing an arrangement of magnetic layers in themagnetoresistive device of FIG. 7(a).

FIG. 8 is a process drawing showing a method for producing themagnetoresistive device of FIG. 7.

FIG. 9 is a graph showing a MR curve for a magnetoresistive device ofthe present invention.

FIG. 10 is a graph showing an example of the applied bias dependency ofnormalized MR for a magnetoresistive device of the present invention.

FIG. 11 is a graph showing an example of the applied bias dependency ofthe junction resistance for a magnetoresistive device of the presentinvention.

FIG. 12 is a graph showing another example of the applied biasdependency of normalized MR for a magnetoresistive device of the presentinvention.

FIG. 13 is a graph showing another example of the applied biasdependency of junction resistance for a magnetoresistive device of thepresent invention.

FIG. 14 is a graph showing another example of a MR curve for amagnetoresistive device of the present invention.

FIG. 15 is a graph showing an Auger depth profile of a junction for amagnetoresistive device of the present invention.

FIG. 16 is a magnification of the graph shown in FIG. 15.

FIG. 17 is a graph showing still another example of the applied biasdependency of normalized MR for a magnetoresistive device of the presentinvention.

FIG. 18 is a graph showing a relation between the heating temperatureand normalized MR for a method for producing a magnetoresistive deviceof the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, embodiments of the present invention are describedwith reference to the drawings.

First Embodiment

In the first embodiment, an example of a magnetoresistive device of thepresent invention is described.

FIG. 1(a) shows a plan view of a magnetoresistive device 10 of a firstembodiment. FIG. 1(b) shows a sectional view taken along the line X—X ofFIG. 1(a).

Referring to FIG. 1, a magnetoresistive device 10 includes a substrate11, and a first magnetic layer 12, a high-resistivity layer 13 and asecond magnetic layer 14 laminated one by one on the substrate 11. Inother words, the magnetoresistive device 10 includes thehigh-resistivity layer 13, and the first magnetic layer 12 and thesecond magnetic layer 14 arranged so as to sandwich the high-resistivitylayer 13.

Various substrates may be used for the substrate 11. Specifically, forexample, a single crystal (magnesia, sapphire, STO, etc.), polycrystal(e.g. AlTIC substrate), amorphous (thermal oxide film of silicon), orconductive substrate (or an oxide of alumina or silicon formed on abase) may be employed. The substrate 11 is not limited to theseexamples, and other substrates also may be used as long as the firstmagnetic layer 12 and the second magnetic layer 14 are insulated. Forexample, when the substrate 11 is a conductor, an additional insulatormay be formed between the first magnetic layer 12 and the secondmagnetic layer 14 in a place other than the tunnel junction.

It is preferable that the surface roughness of the substrate 11 is notmore than 1 nm, particularly preferably not more than 0.5 nm. Thesubstrate 11 may have a lower electrode layer or a lower magnetic layeron its surface as needed. The lower electrode layer herein referred tois an electrode for current and voltage to measure the magneticresistance of the device, and a low-resistivity metal such as Pt, Au,Cu, Ru or Al may be used. In this case, it is particularly preferablethat the lower electrode layer consists of a material containing atleast 90 atomic % of Cu. Furthermore, before forming thehigh-resistivity layer (non-magnetic layer), to smooth the surface ofthe lower electrode layer, ions in a cluster form (e.g. cluster of aninert gas such as Ar) may be irradiated at a low angle with respect tothe surface of the lower electrode layer. Furthermore, the firstmagnetic layer 12 may serve as the lower electrode layer.

Furthermore, a magnetic perovskite oxide, FeCo, Fe or the like havinghigh spin polarizability may be used for the lower magnetic layer.Furthermore, when forming a spin valve magnetoresistive device, to makethe first magnetic layer 12 or the second magnetic layer 14 to be apinned layer, a conductive antiferromagnetic material consisting of acompound of at least one element selected from Pt, Ir, Cr, Pd, Ru andRe; and Mn (e.g. PtMn or IrMn) may be used. Also, Co-basedalloy/Ru/Co-based alloy known as a synthetic structure may be used. Inthis case, the Ru layer has a thickness of 0.6 to 0.8 nm. The Co-basedalloy contains at least 50% Co, and for example, Co, CoPt or CoPtCr maybe used.

The first magnetic layer 12 and the second magnetic layer 14 essentiallyconsist of magnetic metals and contain, for example, at least one metalelement M selected from Fe, Ni and Co. Specifically, these layerscontain, for example, Fe, Co, Ni, a FeCo alloy, a FeNi alloy or a CoFeNialloy. Particularly, it is preferable that the amount of nickel in theFeNi alloy is from 30 to 80%, and the amount of Co in the FeCo alloy isat least 10%. Furthermore, in the first magnetic layer 12, it ispreferable that the element R_(CP) is included in these materials. Otherthan these materials, AMnSb (A is at least one selected from Ni, Cu andPt) also may be used. Furthermore, materials such as LaSrMnO, CrO₂ andFe₃O₄ that are oxides but exhibit high spin polarizability also may beused.

The high-resistivity layer (non-magnetic layer) 13 is a barrier forpassing tunneling electrons between the first magnetic layer 12 and thesecond magnetic layer 14. The high-resistivity layer 13 may passthermoelectrons in addition to tunneling electrons. In themagnetoresistive device 10, a current electrode and a voltage electrodeare connected to each of the first magnetic layer 12 and the secondmagnetic layer 14, and a magnetic resistance is measured by a four-probemethod. In the magnetoresistive device 10, a tunneling current flowsthrough a portion where the first magnetic layer 12 and the secondmagnetic layer 14 cross each other. Hereinafter, the area of thiscrossing portion may be referred to as a cross-sectional area of thedevice.

The high-resistivity layer 13 contains an element L_(ONC) that is atleast one selected from oxygen, nitrogen and carbon as a constituentelement. Specifically, a high-resistivity layer containing at least oneselected from an oxide, a nitride and a carbide may be used as thehigh-resistivity layer 13. More specifically, for example, a layerconsisting of a high-resistivity material having a high bandgap of atleast 1 eV such as Al₂O₃, AlN, BN, SiO₂, Si₃N₄, SiC, (AlGa)N or (AlB)Nmay be used. Moreover, a layer consisting of a composite of thesematerials, or multiple layers of these materials may be used. Theamounts of oxygen, nitrogen and carbon in these materials may deviatefrom their stoichiometric ratios by about 5%. Furthermore, thenon-magnetic layer 13 may have a multi-layered structure in which alayer (not more than 1 nm in thickness) consisting of a non-magneticmetal material or a magnetic metal material is sandwiched betweenhigh-resistivity materials. Furthermore, a layer (not more than 0.5 nmin thickness) consisting of a non-magnetic metal may be inserted in thehigh-resistivity layer 13. The thickness of the high-resistivity layer13 is, for example, from 0.2 nm to 5 nm, and particularly preferablyfrom 0.5 nm to 2.5 nm.

In the magnetoresistive device 10, at least one layer A (preferably bothlayers) selected from the first magnetic layer 12 and the secondmagnetic layer 14 contains at least one metal element M selected fromFe, Ni and Co, and an element R_(CP) different from the metal element M.Specifically, for example, a magnetic layer consisting of Fe, Si and Alor a layer containing the above-described magnetic materials and anelement R_(CP) may be used as the layer A. It is preferable that thelayer A contains at least 0.1 atomic % of the element R_(CP),particularly preferably at least 10 atomic % of the element R_(CP). Theelement R_(CP) in the layer A may be or may not be in a solid solutionstate with the metal element M. The element R_(CP) in the layer A mayform a compound by combining with the element L_(ONC).

It is preferable that the layer A contains the element R_(CP) so thatthe concentration of the element R_(CP) is high on the side of thehigh-resistivity layer 13. In this case, the concentration of theelement R_(CP) may increase gradually to the side of thehigh-resistivity layer 13. Also, the layer A may have a two-layeredstructure consisting of a layer containing the element R_(CP) and alayer not containing the element R_(CP).

Furthermore, the second magnetic layer 14 may be formed after formingthe high-resistivity layer 13, and at least a portion of thehigh-resistivity layer 13 contacting the second magnetic layer 14 maycontain an aluminum oxide as a main component. In this case, it ispreferable that a current is passed so that the first magnetic layer 12is positive and the second magnetic layer 14 is negative. For example,the aluminum oxide may be Al₂O₃.

Furthermore, at least a portion of the high-resistivity layer 13 may beformed by forming a film containing the metal element M and the elementR_(CP), and then reacting the surface of the film with the elementL_(ONC). In this case, it is preferable that a current is passed so thatthe first magnetic layer 12 is negative and the second magnetic layer 14is positive.

The element R_(CP) is characterized by that it combines with the elementL_(ONC) more easily in terms of energy than the metal element M. Forexample, (1) an element having a larger free energy in negative forforming an oxide by combining with one molecule of oxygen than the metalelement M, (2) an element having a larger free energy in negative forforming a nitride by combining with one molecule of nitrogen than themetal element M, or (3) an element having a larger free energy innegative for forming a carbide by combining with one molecule of carbonthan the metal element M may be used as the element R_(CP).Specifically, at least one element selected from Si, Ge, Al, Ga, Cr, V,Nb, Ta, Ti, Zr, Hf. Mg and Ca may be used as the element R_(CP).

In the magnetoresistive device 10, when forming the high-resistivitylayer 13 or using the device, the element R_(CP) in the layer A capturesthe element L_(ONC) diffusing from the high-resistivity layer 13 to forma compound. As a result, in the magnetoresistive device 10, formation ofan antiferromagnetic material such as Fe₂O₃ or CoO or a magneticmaterial having low spin polarizability such as Fe₄N or FeC in the layerA can be prevented. Thus, according to the magnetoresistive device 10,the thickness of the high-resistivity layer can be made sufficientlysmall, so that a device having a low junction resistance and a highmagnetic resistance can be obtained.

The magnetoresistive device shown in FIG. 1 is only one example, and themagnetoresistive device of the present invention may have otherstructures. As an example of a structure different from themagnetoresistive device 10, a plan view of the magnetoresistive device10 a is shown in FIG. 2(a). Furthermore, a sectional view taken alongthe line Y—Y of FIG. 2(a) is shown in FIG. 2(b).

Referring to FIG. 2, the magnetoresistive device 10 a includes asubstrate 11, and a first magnetic layer 12 a, a high-resistivity layer13 a and a second magnetic layer 14 laminated one by one on thesubstrate 11. The first magnetic layer 12 a and the second magneticlayer 14 are arranged so as to sandwich the high-resistivity layer 13 a.

Because the substrate 11 and the second magnetic layer 14 are the sameas those in the magnetoresistive device 10, overlapped explanationsthereof are omitted. The high-resistivity layer 13 a is formed byreacting a portion of the first magnetic layer 12 a with the elementL_(ONC), and has the same function as the high-resistivity layer 13.That is, in the magnetoresistive device 10 a, at least a portion of thehigh-resistivity layer 13 is formed by forming a film containing themetal element M and the element R_(CP), and then reacting the surface ofthe film with the element L_(ONC).

In the magnetoresistive device 10 a, it is preferable that a current ispassed so that the first magnetic layer 12 a is negative and the secondmagnetic layer 14 is positive.

According to the magnetoresistive device 10 a, the same effect as thatof the magnetoresistive device 10 is obtained.

Second Embodiment

In the second embodiment, an example of the method for producing amagnetoresistive device according to the present invention is described.With respect to the same parts and elements as those described in thefirst embodiment, the same numerals are applied, and overlappedexplanations thereof are omitted.

The method of the second embodiment includes:

(a) forming a first magnetic layer 12 a located on a substrate 11, and ahigh-resistivity layer 13 located on the first magnetic layer 12 a andcontaining at least one element L_(ONC) selected from oxygen, nitrogenand carbon; and

(b) forming a second magnetic layer 14 on the high-resistivity layer 13.The first magnetic layer 12 a contains at least one metal element Mselected from Fe, Ni and Co, and contains an element R_(CP) differentfrom the metal element M. As described in the first embodiment, theelement R_(CP) combines with the element L_(ONC) more easily in terms ofenergy than the metal element M. It is preferable that the secondmagnetic layer 14 also contains the element R_(CP).

In the following, the above-mentioned method is described further withmore specific four methods. In FIGS. 3 to 6, only the portion where thefirst magnetic layer and the second magnetic layer cross each other isillustrated.

[First Method]

FIG. 3 shows an example of the production process of the first method.In the first method, first, as illustrated in FIG. 3(a), a magneticlayer 32 containing a metal element M is formed on a substrate 11.Specifically, a layer consisting of at least one selected from Fe, Niand Co may be used as the magnetic layer 32. The magnetic layer 32 maybe formed, for example, by a film-forming method such as evaporationusing a metal mask, sputtering, MBE, laser ablation, high-frequencymagnetron sputtering, direct current sputtering, facing targetsputtering, or ion beam sputtering. Any of the following layers such asa magnetic layer or a high-resistivity layer also may be formed by thesame film-forming method.

Then, as illustrated in FIG. 3(b), a layer B containing an elementR_(CP) is formed on the magnetic layer 32. The layer B can be formed,for example, using a metal mask having a square open hole.

Then, as illustrated in FIG. 3(c), a portion of the surface of the layerB is allowed to react with an element L_(ONC) to form a high-resistivitylayer 13. That is, the high-resistivity layer 13 is formed by oxidizing,nitriding, or carbonizing the element in the surface of the layer B. Toreact the surface of the layer B with the element L_(ONC), for example,the layer B may be treated in a gas atmosphere containing the elementL_(ONC). Examples of the gas atmosphere containing the element L_(ONC)include oxygen gas atmosphere, oxygen plasma atmosphere, nitrogen gasatmosphere, nitrogen plasma atmosphere, oxygen radical atmosphere,nitrogen radical atmosphere, ozone atmosphere, and the like. In the stepof FIG. 3(c), the kind of a gas, partial pressure of a gas, plasmadensity, substrate temperature, and the like are controlled to carry outthe treatment.

Then, as illustrated in FIG. 3(d), by heating the substrate on which thehigh-resistivity layer 13 is formed at a temperature of at least 50° C.but not higher than 350° C., unreacted parts of the element R_(CP) notincluded in the high-resistivity layer 13 are allowed to diffusemutually with the metal element M in the magnetic layer 32, therebyforming a first magnetic layer 32 a containing the element R_(CP) inwhich the concentration of the element R_(CP) gradually increases to theside of the high-resistivity layer 13.

Then, as illustrated in FIG. 3(e), a second magnetic layer 14 is formedon the high-resistivity layer 13. The second magnetic layer 14 can beformed by the same method as the magnetic layer 32. Thus, themagnetoresistive device 10 described in the first embodiment can beproduced.

In the first method, heating of the substrate (diffusion of the elementR_(CP)) may be carried out after forming the second magnetic layer 14.The substrate also may be heated simultaneously with the step of formingthe magnetic layer 32, so that the element R_(CP) is allowed to diffuseinto the magnetic layer 32 when forming the layer B. In this case, theoutermost surface of the layer B is oxidized with residual oxygen orwater in the vacuum device, etc. to form a high-resistivity layer. Thus,essentially, the step of forming a high-resistivity layer, the step offorming a layer consisting of unreacted R_(CP), and the step ofdiffusing unreacted R_(CP) proceed simultaneously. These steps are allincluded in the first method. Furthermore, fine processing for formingthe device also may be carried out between these steps.

[Second Method]

In the second method, first, as illustrated in FIG. 4(a), a firstmagnetic layer 12 a is formed on a substrate 11.

Then, as illustrated in FIG. 4(b), a layer C having a thickness of 0.1nm to 2 nm and containing an element R_(CP) is formed on the firstmagnetic layer 12 a.

Then, as illustrated in FIG. 4(c), a high-resistivity layer 13 is formedby reacting the layer C with an element L_(ONC). That is, thehigh-resistivity layer 13 is formed by oxidizing, nitriding, orcarbonizing an element in the layer C. This is the same as the step ofFIG. 3(c). However, the entire layer C is allowed to react with theelement L_(ONC) in the second method.

Then, as illustrated in FIG. 4(d), a second magnetic layer 14 is formedon the high-resistivity layer 13. Thus, the magnetoresistive device 10described in the first embodiment can be produced.

It is preferable that the first magnetic layer 12 a contains the elementR_(CP) so that the concentration of the element R_(CP) graduallyincreases to the side of the high-resistivity layer 13. To form such afirst magnetic layer 12 a, the element R_(CP) may be allowed to diffuseinto the first magnetic layer 12 a in the step of FIG. 4(b) or FIG.4(c).

The first magnetic layer 12 a also may be formed by evaporation orsputtering in which the deposition rates of respective elements arechanged so that the concentration of the element R_(CP) is high on theside of the high-resistivity layer 13 (this also applies to thefollowing methods).

[Third Method]

In the third method, first, as illustrated in FIG. 5(a), a firstmagnetic layer 12 a is formed on a substrate 11. This is the same as thestep of FIG. 4(a).

Then, as illustrated in FIG. 5(b), a high-resistivity layer 13 is formedby depositing an element R_(CP) on the first magnetic layer 12 a in agas atmosphere containing an element L_(ONC). Examples of the gasatmosphere containing an element L_(ONC) include oxygen gas atmosphere,oxygen plasma atmosphere, nitrogen gas atmosphere, nitrogen plasmaatmosphere, oxygen radical atmosphere, nitrogen radical atmosphere,ozone atmosphere, and the like.

In the step of FIG. 5(b), the element R_(CP) may be allowed to diffuseinto the first magnetic layer 12 a so that the concentration of theelement R_(CP) in the first magnetic layer 12 a gradually increases tothe side of the high-resistivity layer 13.

Then, as illustrated in FIG. 5(c), a second magnetic layer 14 is formed.This is the same as the step of FIG. 4(d). Thus, the magnetoresistivedevice 10 described in the first embodiment can be produced.

[Fourth Method]

In the fourth method, as illustrated in FIG. 6(a), a magnetic layer 62containing a metal element M and an element R_(CP) is formed on asubstrate 11. The magnetic layer 62 can be formed by the same method asthe first magnetic layer 12 a.

Then, as illustrated in FIG. 6(b), by reacting the surface of themagnetic layer 62 with an element L_(ONC), a first magnetic layer 12 aand a high-resistivity layer 13 are formed. That is, in the step of FIG.6(b), the high-resistivity layer 13 is formed by oxidizing, nitriding,or carbonizing the surface of the magnetic layer 62. To react thesurface of the magnetic layer 62 with the element L_(ONC), the magneticlayer 62 may be treated in a gas atmosphere containing the elementL_(ONC) in the same way as the step 4(c).

In the step of FIG. 6(b), it is preferable that the element R_(CP) isallowed to diffuse into the first magnetic layer 12 a so that theconcentration of the element R_(CP) in the first magnetic layergradually increases to the side of the high-resistivity layer 13. Inthis case, it is preferable that when reacting the surface of themagnetic layer 62 with the element L_(ONC), the surface of the magneticlayer 62 is heated at a temperature of at least 50° C. but not higherthan 800° C. (preferably, 100° C. to 500° C.).

Then, as illustrated in FIG. 6(c), the second magnetic layer 14 isformed. This is the same as the step of FIG. 4(d). Thus, themagnetoresistive device 10 a described in the first embodiment can beproduced.

In the above-mentioned production method of the second embodiment, whenforming the high-resistivity layer 13, the element L_(ONC) diffusingfrom the high-resistivity layer 13 to the first magnetic layer 12 a iscaptured by the element R_(CP) in the first magnetic layer 12 a. Thus,according to the above method, a magnetoresistive device having a lowjunction resistance and a high magnetic resistance can be produced.

The first magnetic layer 12 a in which the concentration of the elementR_(CP) is high on the side of the high-resistivity layer 13 also may beformed by the following method. First, the first magnetic layer 12 a andthe high-resistivity layer 13 are formed. Then, under the environment inwhich the kind of gas, partial pressure of a gas, plasma density,substrate temperature and the like are controlled, the surface of thehigh-resistivity layer 13 is oxidized or nitirided, a gradient ofchemical potential of oxygen ions or nitrogen ions is formed. This makespossible that the concentration of the element R_(CP) graduallyincreases to the side of the high-resistivity layer 13 in the firstmagnetic layer 12 a.

Although the method using a metal mask has been described in the aboveembodiment, general fine processing technology used for semiconductorsor the like also may be employed. By using such fine processingtechnology, a magnetoresistive device used for magnetic reproducingheads or MRAM devices can be produced.

Third Embodiment

In the third embodiment, a magnetic component of the present inventionis described.

The magnetic component of the present invention includes amagnetoresistive device. The magnetoresistive device is obtained byheating the magnetoresistive device of the present invention describedin the first embodiment at a temperature of at least 200° C.

EXAMPLES

The present invention is described further below in detail withreference to examples.

Example 1

In Example 1, the magnetoresistive device 10 of the present inventionwas produced by the method shown in FIG. 3. In Example 1, the elementR_(CP) in the layer B was allowed to diffuse by heating after formingthe second magnetic layer.

In Example, 1, four devices having cross-sectional areas of 20×20,50×50, 100×100, and 200×200 (μm×μm) were produced. The magnetic layersand the layer B were formed by RF magnetron sputtering using a metalmask. The degree of vacuum in the sputter equipment when forming a filmwas 6.65×10⁻⁴ Pa (5×10⁻⁶ Torr). The film-forming rate for each layer wasabout 10 nm/min.

In Example 1, as the substrate, a Si substrate on which a SiO₂ film (300nm in thickness) was formed by thermal oxidation was used.

(1) A metal mask was placed on the Si substrate, and a film consistingof Fe (20 nm in thickness) was formed as the magnetic layer 32. Then,the sputter equipment was opened in the air, and the metal mask wasexchanged.

(2) On the magnetic layer 32, a layer consisting of Si (0.5 nm inthickness) and a layer consisting of Al (1.0 nm in thickness) wereformed one by one as the layer B.

(3) The substrate on which the layer B was formed was allowed to standat a substrate temperature of 60° C. in a pure oxygen atmosphere for onehour, and the surface of the layer B was oxidized. Thus, thehigh-resistivity layer 13 was formed. Then, the sputter equipment wasopened in the air, and the metal mask was exchanged.

(4) On the high-resistivity layer 13, a layer consisting of Fe₅₀Co₅₀ (20nm in thickness) was formed as the second magnetic layer 14. At thistime, MR was measured (applied magnetic field: ±79,600 A/m (±1000 Oe)).

(5) The substrate on which the second magnetic layer 14 was formed washeated at 250° C. in vacuum for 1 hour. The thus obtainedmagnetoresistive device was measured for MR (applied magnetic field:±79,600 A/m (±1000 Oe)).

In the MR curve measured after the step (4), the MR increased rapidly atabout 2,390 A/m (about 30 Oe), and the MR decreased rapidly at 23,900A/m (300 Oe). This corresponds to the double hysteresis loops of the MHcurve of this device measured by VSM (vibration sample magnetometer),and showed a typical tendency of differential coercive force. The valueof 2,390 A/m (300 Oe) corresponds to the coercive force of Fe, and thevalue of 23,900 A/m (300 Oe) corresponds to the coercive force of theCoFe alloy. The MR ratio at ±79,600 A/m (±1000 Oe) and at zero magneticfield was about 13 to 16% in any cross-sectional area of the device.Furthermore, the device resistance normalized for the cross-sectionalarea of 1 μm×1 μm was about 1 MΩ irrespective of the cross-sectionalarea of the device.

In the MR curve measured after the step (5), the rise field and fallfield of MR was decreased to 1,990 A/m (25 Oe) and 21,500 A/m (270 Oe),respectively. Furthermore, in any cross-sectional area of the device,the MR ratio was increased up to about 20 to 23%. Furthermore, after thestep (5), the device resistance at zero magnetic field was decreased to300 KΩ.

The interface of the high-resistivity layer before and after the heatingin the step (5) was observed by an Auger depth profile. The resultshowed that the interface between Fe and Si, which was sharp right afterforming the films, was broad after the heating so that the concentrationof Si was high on the side of the high-resistivity layer. Furthermore,when investigating the change in oxidation condition before and afterthe heating by XPS, only the peak of an aluminum oxide was observed bothbefore and after heating. Furthermore, when investigating the change inthe bonding condition before and after the heating by X-ray diffraction,it was found that the peak of Fe right after forming the films shiftedto the side of the FeSi alloy after the heating.

These results show that at least Si remained at the interface betweenthe first magnetic layer and the high-resistivity layer right afterforming the films, and Si was allowed to diffuse mutually with Fe in thefirst magnetic layer 12 by the heating.

It is considered that the change in MR before and after the heating wascaused by the deletion of spin memory due to unreacted Si before theheating and the increase in spin polarizability at the interface of thehigh-resistivity layer due to the heating.

Thus, in Example 1, a magnetoresistive device having a low deviceresistance and a high MR was obtained.

Example 2

In Example 2, the magnetoresistive device 10 of the present inventionwas produced by the method shown in FIG. 4.

In Example 2, four devices having cross-sectional areas of 20×20, 50×50,100×100, and 200×200 (μm×μm) were produced. The magnetic layers and thelayer B were formed by RF magnetron sputtering using a metal mask. Thedegree of vacuum in the sputter equipment when forming a film was6.65×10⁻⁴ Pa (5×10⁻⁶ Torr). The film-forming rate for each layer wasabout 10 nm/min.

In Example 2, as the substrate, a Si substrate on which a SiO₂ film (300nm in thickness) was formed by thermal oxidation was used.

(1) A metal mask was placed on the Si substrate, and a FeSiAl layerconsisting of Fe (85 mass %)—Si (10 mass %)—Al (5 mass %) (20 nm inthickness) was formed as the first magnetic layer 12 a. Then, thesputter equipment was opened in the air, and the metal mask wasexchanged.

(2) On the FeSiAl layer, an aluminum layer (1.0 nm in thickness) wasformed as the layer C.

(3) The substrate on which the aluminum layer was formed was allowed tostand at a substrate temperature of 60° C. in a pure oxygen atmospherefor 24 hours to oxidize the aluminum layer so that a high-resistivitylayer was formed. Then, the sputter equipment was opened in the air, andthe metal mask was exchanged.

(4) On the high-resistivity layer, a layer consisting of Fe₅₀Co₅₀ (20 nmin thickness) was formed as the second magnetic layer 14.

In Example 2, as a comparative example, a magnetoresistive device usinga layer consisting of Fe (20 nm in thickness) in place of the FeSiAllayer as the magnetic layer 32 also was produced. The thus obtainedmagnetoresistive device was measured for MR (applied magnetic field:±79,600 A/m (±1000 Oe)).

With respect to both the devices using the FeSiAl alloy as the magneticlayer 32 and the device using Fe as the magnetic layer 32, it was foundthat the obtained MR curve was a differential coercive force typecorresponding to hysteresis loops of VSM. In the device using Fe for themagnetic layer 32, the MR ratio at ±79,600 A/m (±1000 Oe) and at zeromagnetic field was about 7% in any cross-sectional area of the device.On the other hand, in the device using the FeSiAl alloy for the magneticlayer 32, the MR ratio was about 20%, which was a high value.Furthermore, in the device using the FeSiAl alloy, the normalizedresistance was about 2 MΩ in any cross-sectional area of the device, anda relatively low resistance was exhibited.

Auger depth profiles of respective devices were observed. As a result,it was found that in the device using Fe for the magnetic layer 32,oxygen was spread broadly from the interface between the aluminum oxideas a high-resistivity layer and the first magnetic layer (mainly Fe) tothe side of the first magnetic layer. On the other hand, in the deviceusing FeSiAl for the magnetic layer 32, Al and Si having concentrationgradients were observed in high concentrations in the vicinity of theinterface between the aluminum oxide and the first magnetic layer. Also,a high concentration of oxygen was observed at the same depth as whereSi or Al was distributed in a high concentration. In a deeper place, itwas observed that the amount of oxygen decreased more sharply than inthe comparative example.

Furthermore, in the comparative example using Fe, when investigating theoxidation condition by XPS, Fe oxides were observed. On the other hand,in the magnetoresistive device using FeSiAl, only Si oxides and Aloxides were observed.

These results show that at the interface between FeSiAl as the magneticlayer and the aluminum oxide as the high-resistivity layer, diffusion ofoxygen into the magnetic layer was inhibited by Si and Al, so that theoxidation of the metal element M that seems to result in spin inversionwas inhibited. Thus, it appears that a very high MR can be realized byusing a magnetic layer containing the element R_(CP) such as FeSiAl,even though the polarizability of FeSiAl is lower than that of Fe.

As mentioned above, according to the present invention, amagnetoresistive device having a low resistance and a high MR isrealized. Furthermore, the magnetoresistive device produced by the abovemethod was so excellent that the irregularity in the device propertieswas about 10% in an average of ten samples.

In Example 2, although FeSiAl was used for the first magnetic layer, thesame effect is obtained using other elements as long as the metalelement M and the element R_(CP) are contained in the first magneticlayer.

Example 3

In Example 3, a device was formed using a thin-film formation withmagnetron sputtering and pattern processing with photolithography andion milling.

In Example 3, six magnetoresistive devices with different structureswere formed. The structures of the devices formed in Example 3 are shownin Tables 1 and 2.

TABLE 1 Thick- ness of SiO₂ in Thickness Oxidation conditions the sub-of the first Thickness Oxygen Sample strate magnetic of Al layerpressure Time Substrate No. [nm] layer [nm] [nm] [Pa] [min] temperatureX1 300 25 0.8 34580 20 Room temp. X2 300 25 0.8 34580 60 Room temp. X3300 20 1.0 34580 60 Room temp. X4 500 20 0.6 34580 60 Room temp. X5 50020 1.0 34580 60 90° C. X6 500 20 0.8 34580 60 90° C.

TABLE 2 Thickness of Second magnetic layer interlayer Sample CompositionThickness insulating No. [atomic %] [nm] film [nm] Structure of theupper electrode X1 Co₅₀Fe₅₀ 11 200 Au: 20 nm Al: 200 nm Au: 50 nm X2Co₅₀Fe₅₀ 11 200 Au: 20 nm Al: 200 nm Au: 50 nm X3 Co₅₀Fe₅₀  4 200 Pt: 10nm Cu: 200 nm Ta: 50 nm X4 Co₉₀Fe₁₀ 10 300 Pt: 5 nm Cu: 400 nm Ta: 50 nmX5 Co₃₀Fe₇₀ 10 300 Pt: 5 nm Cu: 400 nm Pt: 50 nm X6 Co₃₀Fe₇₀ 10 300 Pt:5 nm Cu: 400 nm Ta: 50 nm

FeSiAl alloy consisting of Fe (85 mass %)—Si (10 mass %)—Al (5 mass %)was used for the first magnetic layer. In the sample X6, a pinned layer(25 nm in thickness) consisting of Ir₂₀Mn₈₀ (atomic %) was formedbetween the second magnetic layer and the interlayer insulating layer.

FIG. 7(a) is an enlarged view of a functional part of a magnetoresistivedevice 70 produced in Example 3. Referring to FIG. 7(a), themagnetoresistive device 70 includes a substrate 71; a first magneticlayer 72, a high-resistivity layer 73, a second magnetic layer 74 and anupper electrode 75 formed one by one on the substrate 71; and aninterlayer insulating layer 76 located at the side faces of thehigh-resistivity layer 73 and the second magnetic layer 74. FIG. 7(b) isa plan view showing an arrangement of the first magnetic layer 72 andthe second magnetic layer 74.

FIG. 8 shows a production process for the method of Example 3. In themethod of Example 3, magnetron sputtering was used for forming thinfilms. The degree of vacuum in the sputter equipment when forming thinfilms was not higher than about 4×10⁻⁴ Pa (3×10⁻⁶ Torr). Thefilm-forming rate was about 0.1 to 0.2 nm/sec.

First, on the substrate 71, the first magnetic layer 72 and an aluminumlayer consisting of Al were formed one by one. As the substrate 71, a Sisubstrate on which SiO₂ was formed was used. Then, oxygen was introducedin the sputter equipment to oxidize the aluminum layer, and thehigh-resistivity layer 73 was formed. Then, as illustrated in FIG. 8(a),the second magnetic layer 74 was formed on the high-resistivity layer73.

Next, as illustrated in FIG. 8(b), by leaving a resist in the shape of ajunction by photolithography and thereafter milling portions other thanthe junction, a portion of the first magnetic layer 72 was removed overthe high-resistivity layer 73.

Then, as illustrated in FIG. 8(c), an interlayer insulating layer 76consisting of SiO₂ was formed by lift-off technology, and side faces ofthe junction were insulated.

Then, as illustrated in FIG. 8(d), after cleaning the surface of thejunction as needed, the upper electrode 75 was formed. The upperelectrode 75 also may be formed between the steps of FIG. 8(b) and FIG.8(c).

In FIG. 8, a magnetoresistive device in which the first magnetic layer72 functions as a lower electrode has been described. However, the sameresult was obtained when further a lower electrode was formed below thefirst magnetic layer. In this case, the same effect was obtained evenwhen a portion of the lower electrode was removed over the firstmagnetic layer by the milling in the step of FIG. 8(b).

With respect to the magnetoresistive device produced by the abovemethod, a MR curve of the sample X2, which is a typical MR curve, isshown in FIG. 9. Furthermore, with respect to the device of the sampleX1 before and after the heating, the applied bias dependency of MR isshown in the graph of FIG. 10, and the applied bias dependency ofjunction resistance is shown in the graph of FIG. 11. Furthermore, withrespect to the sample X2 before and after the heating, the applied biasdependency of MR is shown in the graph of FIG. 12, and the applied biasdependency of junction resistance is shown in the graph of FIG. 13. Theheating was carried out after forming the multi-layered film, or afterprocessing it into the shape of a device. When the heating is carriedout right after forming the multi-layered film, it is preferable thatthe heating is performed in a vacuum under a magnetic field of at least79,600 A/m (1000 Oe). Furthermore, when the heating is carried out afterprocessing it into the shape of a device, taking into account theinfluence of an anti-magnetic field, it is preferable that the heatingis performed in vacuum under a magnetic field of at least 398,000 A/m(5000 Oe). The graphs shown in FIGS. 10 to 13 are for devices having across-sectional area of 3 μm×3 μm. Furthermore, in the graphs of FIGS.10 to 13, the applied bias when passing a current from the secondmagnetic layer to the first magnetic layer (i.e. when passing electronsfrom the first magnetic layer to the second magnetic layer) isdetermined negative. In the junction resistance, different fromconventional devices, only a little asymmetry was observed, but no shiftof the peak value was observed. However, in the MR value, a shift of thepeak MR value in the direction of negative bias was observed, and aninhibition of decrease in MR at negative bias was observed. As a result,an excellent characteristic was obtained such that the bias at which MRwas decreased by half exceeded 500 mV. The same results were obtained inany of the samples X1 to X6 in Tables 1 and 2. With respect to thesamples X1 to X6, the bias at which MR was decreased by half when a biaswas applied from the first magnetic layer to the second magnetic layeris shown in Table 3.

TABLE 3 Sample Bias at which MR is No. Peak MR value (%) Decreased byhalf [mV] X1 11.8 510 X2 16.2 550 X3  7.8 510 X4 10.9 650 X5 13.5 570 X6 6.0 500

When a magnetic layer having at least one element selected from Fe, Coand Ni as a basic component and having at least 0.5 mass % of at leastone element selected from Al, Si, Ge, Ga, Cr, V, Nb, Ta, Ti, Zr, Hf, Mgand Ca as an additional component was used as the first magnetic layer,the same effect was obtained. Furthermore, when a layer consisting of atleast one element selected from Si, Ge, Ga, Cr, V, Nb, Ta, Ti, Zr, Hf,Mg and Ca was used in place of the aluminum layer that becomes thehigh-resistivity layer 73, the same effect was obtained.

Example 4

In Example 4, a magnetoresistive device of the present invention wasproduced by the method illustrated in FIG. 6.

In Example 4, four devices having cross-sectional areas of 20×20, 50×50,100×100, and 200×200 (μm×μm) were produced. Each layer was formed by RFmagnetron sputtering. The degree of vacuum in the sputter equipment whenforming a film was 6.65×10⁻⁴ Pa (5×10⁻⁶ Torr). The film-forming rate foreach layer was about 10 nm/min.

In Example 4, as the substrate, a Si substrate on which a SiO₂ film (300nm in thickness) was formed by thermal oxidation was used.

(1) A metal mask was placed on the Si substrate, and a FeSiAl layerconsisting of Fe (85 mass %)—Si (10 mass %)—Al (5 mass %) was formed asthe magnetic layer 62. The substrate temperature when forming the layerwas 450° C. The thickness of the FeSiAl layer was 20 nm.

(2) Pure oxygen of 13.3 Pa (100 mTorr) was introduced into the sputterequipment. Then, the substrate was allowed to stand in the pure oxygenatmosphere for 0.5 hour while maintaining the substrate temperature at450° C. Thus, the surface of the FeSiAl layer was oxidized, and ahigh-resistivity layer was formed. Then, the sputter equipment wasopened in the air, and the metal mask was exchanged.

(3) As the second magnetic layer, a NiFe layer (20 nm in thickness)consisting of Ni₈₀Fe₂₀ was formed at room temperature. Thus, amagnetoresistive device of the present invention was formed. For thethus obtained device, MR was measured (applied magnetic field: ±79,600A/m (±1000 Oe)).

It was found that the MR curve measured after the step (3) was adifferential coercive force type corresponding to the hysteresis loop ofFeSiAl and the hysteresis loop of NiFe. The MR ratio in the device wasfrom 27 to 30%, which was very high. Furthermore, the resistance of thedevice was 30 kΩ, which was very low.

FIG. 14 shows an example of the MR curve of the device. Both the riseand fall of the MR curve are gentle. Although from the MR curves ofrespective magnetic films it appears that magnetized FeSiAl and NiFe arenot completely antiparallel, it is understood that a very high MR isrealized. Furthermore, although both FeSiAl and NiFe have lower spinpolarizability than Fe or FeCo, a higher MR and a lower resistance thanExample 1 or 2 were obtained.

When observing an Auger depth profile of the device, an oxide layer ofthe FeSiAl layer (the first magnetic layer) having particularly highconcentrations of Si and Al was observed at the interface between theFeSiAl layer and the NiFe layer. Furthermore, the oxygen concentrationchanged sharply in this layer. Taking into consideration the change inthe composition ratio of Si and Al, it seems that particularly aluminumdiffused from inside of the FeSiAl layer into the high-resistivitylayer.

These results show that a high-resistivity layer can be formed bynatural oxidation (or thermal oxidation) of a magnetic layer containingthe element R_(CP) (such as FeSiAl), and a TMR device having anexcellent MR and a low resistance can be obtained.

Although FeSiAl was used for the first magnetic layer in Example 4, thesame effect is obtained as long as the first magnetic layer contains atleast one metal element M selected from Fe, Co and Ni, and at least oneelement R_(CP) selected from Si, Ge, Al, Ga, Cr, V, Nb, Ta, Ti, Zr, Hf,Mg and Ca (This also applies to the following examples).

Furthermore, in Example 4, the FeSiAl layer was formed while heating thesubstrate. However, the FeSiAl layer also may be oxidized, nitrided, orcarbonized by heating the substrate at a temperature of at least 50° C.but not higher than 800° C. after forming the FeSiAl layer at roomtemperature. The oxidation or nitriding may be carried out by treatingit in an oxygen atmosphere, oxygen plasma atmosphere, nitrogenatmosphere, or nitrogen plasma atmosphere, while heating the substrate.The gas pressure at this time is, for example, from 13.3 mPa (0.1 mTorr) to 1.11×10⁵ Pa (1 atm.). In this method, a tunnel junction alsocan be formed in the same way as in Example 4 (This also applies to thefollowing examples.).

Example 5

In Example 5, a magnetoresistive device of the present invention wasproduced by the method described in the second embodiment. In Example 5,each layer was formed by the same film-forming method as in Example 1.The same Si substrate as in Example 1 was used. The device of Example 5had a cross-sectional area of 100 μm×100 μm.

(1) A metal mask was placed on the Si substrate, and a FeSiAl layerconsisting of Fe (85 mass %)—Si (10 mass %)—Al (5 mass %) was formed asthe first magnetic layer 12 a. The substrate temperature when formingthe layer was 430° C. The thickness of the FeSiAl layer was 20 nm.

(2) Pure oxygen of 13.3 Pa (100 mTorr) was introduced into the sputterequipment. Then, the substrate was allowed to stand in the pure oxygenatmosphere for 1 hour while maintaining the substrate temperature at430° C. Thus, the surface of the FeSiAl layer was oxidized, and ahigh-resistivity layer was formed. Then, the sputter equipment wasopened in the air, and the metal mask was exchanged.

(3) As the second magnetic layer, a CoFe layer (11 nm in thickness)consisting of Co₅₀Fe₅₀ was formed at room temperature. For the thusobtained magnetoresistive device, MR was measured (applied magneticfield: ±79,600 A/m (±1000 Oe)).

It was found that the MR curve measured when completing the step (3) wasa differential coercive force type corresponding to a hysteresis loop ofFeSiAl and a hysteresis loop of CoFe. After the step (3), because thejunction resistance of 100 square micron was not sufficiently high withrespect to the sheet of FeSiAl serving as an electrode, the MR curveincluded a shape effect. When this device was heated at 250° C., thejunction resistance increased, and a normal tunnel magnetic resistancewas able to be measured. The MR after the heating was about 20%, whichwas very high.

An Auger depth profile after the heating is shown in FIG. 15. Amagnification of the longitudinal axis of FIG. 15 is shown in FIG. 16.As illustrated, CeFe is oxidized since the outermost surface of thesample is in contact with the air. However, the presence of an oxidelayer at the surface of FeSiAl is confirmed toward the depth direction(i.e. the substrate direction, the right side of the graph). In FIG. 16,it is observed that particularly, the peak of the intensity distributionof aluminum is shifted slightly to the substrate side with respect tothe intensity distribution of oxygen forming the high-resistivity layer,and the intensity of aluminum is decreased in the FeSiAl layer. Thisseems to be because aluminum has diffused mainly from inside of theFeSiAl layer.

These results show that by natural oxidation (or thermal oxidation) of amagnetic layer containing an element R_(CP) such as FeSiAl, ahigh-resistivity layer is formed, and a TMR device having an excellentMR and a low resistance is obtained.

Example 6

In Example 6, as for the magnetoresistive device of Example 5, the biasdependency of MR property was investigated by changing the direction ofan applied bias (direction of a current). The results are shown in FIG.17.

In FIG. 17, the bias is considered positive when a current is passedfrom FeCo to FeSiAl. Inversely, the bias is considered negative when acurrent is passed from FeSiAl to FeCo. The longitudinal axis of FIG. 17shows normalized MR.

In the magnetoresistive device of Example 5, different from Example 3,higher bias stability was obtained when a current was passed from theFeSiAl layer (the first magnetic layer 12 a).

Example 7

In Example 7, the heating temperature dependency of MR was investigatedby further heating the magnetoresistive device of Example 5. The heatingwas carried out in vacuum under zero magnetic field.

The measurement results are shown in FIG. 18. The longitudinal axis ofthe graph shows normalized MR, and the lateral axis of the graph showsheating temperature. The MR is normalized in FIG. 18. Different fromconventional TMR devices, the tunnel structure was maintained afterheating it at a high temperature of 400° C. This shows that themagnetoresistive device of the present invention has high thermalstability.

The magnetoresistive device of the present invention showed acharacteristic in that heating at a temperature of at least 200° C.further increases the MR ratio, or that thermal stability was maintainedat a high temperature.

Having described embodiments of the present invention with reference toexamples, the present invention is not limited to the above-describedembodiments, and may be applied to other embodiments based on thetechnical idea of the present invention.

INDUSTRIAL APPLICABILITY

As mentioned above, in the magnetoresistive device of the presentinvention, decrease in MR due to spin inversion in the vicinity of thehigh-resistivity layer, and deletion of spin memory due to unreactednon-magnetic material (mainly Al) are inhibited. Thus, according to themagnetoresistive device of the present invention, a very thinhigh-resistivity layer can be formed. As a result, a magnetoresistivedevice having a low resistance and a high rate of change inmagnetoresistance is obtained.

The magnetoresistive device of the present invention can be used in awide range of applications such as reproducing heads of magneticrecorders, magnetic sensors, magnetic random access memories (MRAM) orthe like. By using the magnetoresistive device of the present inventionas a reproducing head for magnetic or photomagnetic recording media, ahigh memory density of 15.5 Gbit/cm² (100 Gbit/in²) is realized.Furthermore, by using the magnetoresistive device of the presentinvention, nonvolatile memories corresponding to high frequencies arerealized.

Furthermore, in the method of the present invention for producing amagnetoresistive device, oxygen, nitrogen, carbon or the like diffusingfrom the high-resistivity layer into the first magnetic layer iscaptured by the element R_(CP) when forming the high-resistivity layer.Thus, according to the method of the present invention, amagnetoresistive device having a low resistance and a high rate ofchange in magnetoresistance can be produced easily. Furthermore,according to the method of the present invention, a device with littleirregularity can be produced with high productivity.

What is claimed is:
 1. A magnetoresistive device comprising: ahigh-resistivity layer, a first magnetic layer and a second magneticlayer, the first magnetic layer and the second magnetic layer beingarranged so as to sandwich the high resistivity layer, wherein: a firstside of the high-resistivity layer is in contact with the first magneticlayer, and a second side of the high-resistivity layer is in contactwith the second magnetic layer; the high-resistivity layer is a barrierfor passing tunneling electrons between the first magnetic layer and thesecond magnetic layer, and contains at least one element L_(ONC)selected from oxygen, nitrogen and carbon; at least one layer A selectedfrom the first magnetic layer and the second magnetic layer contains atleast one metal element M selected from Fe, Ni and Co, and an elementR_(CP) different from the metal element M; and the element R_(CP)combines with the element L_(ONC) more easily in terms of energy thanthe metal element M combines with the element L_(ONC).
 2. Themagnetoresistive device according to claim 1, wherein the layer Acontains the element R_(CP) so that a concentration of the elementR_(CP) is high on the side of the high-resistivity layer.
 3. Themagnetoresistive device according to claim 1, wherein the element R_(CP)is at least one element selected from Si, Ge, Al, Ga, Cr, V, Nb, Ta, Ti,Zr, Hf, Mg and Ca.
 4. The magnetoresistive device according to claim 1,wherein the layer A consists of Fe, Si and Al.
 5. The magnetoresistivedevice according to claim 1, wherein the element R_(CP) forms a compoundwith the element L_(ONC) in the vicinity of the high-resistivity layerin the layer A.
 6. The magnetoresistive device according to claim 1,wherein the second magnetic layer is on the high-resistivity layer, anda portion of the high-resistivity layer contacting the second magneticlayer contains an aluminum oxide as a main component.
 7. Themagnetoresistive device according to claim 6, wherein a current ispassed so that the first magnetic layer is positive and the secondmagnetic layer is negative.
 8. The magnetoresistive device according toclaim 1, wherein at least a portion of the high-resistivity layer is afilm comprising the metal element M and the element R_(CP) with asurface of the film containing the element L_(ONC).
 9. Themagnetoresistive device according to claim 8, wherein a current ispassed so that the first magnetic layer is negative and the secondmagnetic layer is positive.